JP2011250306A - Video signal processing apparatus and video signal processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a video signal processing apparatus which excellently processes an image signal for satisfactorily expressing the tone of an image.SOLUTION: The video signal processing apparatus of this embodiment comprises gain control means and gradation smoothing control means. The gain control means controls a gain for correcting the image signal. The gradation smoothing control means controls according to the gain controlled by the gain control means a gradation smoothing parameter for smoothing the gradation of the image corresponding to the image signal.

Description

  Embodiments described herein relate generally to a video signal processing apparatus and a video signal processing method for correcting a video signal.

  A liquid crystal display device such as a digital TV is composed of, for example, a liquid crystal panel and a backlight, and a backlight provided on the back of the liquid crystal panel illuminates the liquid crystal of the liquid crystal panel. A plurality of light sources constituting the backlight are shifting from cold cathode fluorescent lamps to LED (Light Emitting Diode) lights. The LED light is excellent in terms of low power consumption, long life, and brightness control.

  For example, the overall luminance control for collectively controlling the luminance of a plurality of LED lights constituting the backlight according to the video signal, and the luminance of the predetermined number of LED lights in units of the predetermined number of LED lights according to the video signal Area luminance control for controlling the image is known.

JP 2008-203292 A

  If, for example, a predetermined number of LED lights are controlled to have low luminance in accordance with the video signal by area luminance control, the partial video displayed in the partial display area corresponding to the predetermined number of LED lights becomes dark overall. If a bright video is not included in the partial video, such a partially dark partial image may be displayed. However, if this partial video contains a bright video, such an overall dark partial video display will darken the originally bright video in this partial video. It is not a display.

  Therefore, it is considered that the video signal is amplified by area luminance control when, for example, a predetermined number of LED lights are controlled to have low luminance in accordance with the video signal. However, even if the video signal is amplified, the gradation does not change. Therefore, in the case where a bright video is included in the partial video as described above, this bright video is not easy to see.

  An object of the present invention is to provide a video signal processing apparatus and a video signal processing method that are excellent in video signal processing for satisfactorily expressing the contrast of video.

  The video signal processing apparatus according to the embodiment includes gain control means and gradation smoothing control means. The gain control means controls a gain for correcting the video signal. The gradation smoothing control means controls a gradation smoothing parameter for smoothing the gradation of the video corresponding to the video signal in accordance with the gain controlled by the gain control means.

It is a block diagram which shows an example of the video display apparatus which concerns on 1st Embodiment. It is a block diagram which shows an example of the backlight control and video correction module provided in the video display apparatus which concerns on 1st Embodiment. FIG. 3 is a block diagram showing an example of a detailed configuration of a backlight control / video correction module according to the first embodiment. It is a figure which shows an example of the relationship between the output luminance of a video signal determined by the backlight control and video correction module shown in FIG. 2, and input luminance. It is a figure which shows an example of the dark part area and the bright part maximum value which are calculated by the backlight control and image correction module shown in FIG. It is a figure which shows an example of the relationship between the backlight lower limit determined by the backlight control and image | video correction | amendment module shown in FIG. 2, and a dark part area. It is a figure which shows an example of the relationship between the dimming start value determined by the backlight control and image | video correction | amendment module shown in FIG. 2, and a dark part area. FIG. 3 is a diagram illustrating an example of a relationship between a maximum gain determined by a backlight control / video correction module illustrated in FIG. 2 and a bright portion maximum value. 3 is a flowchart illustrating an example of a procedure of backlight control processing by the video display device illustrated in FIG. 1. The block diagram which shows an example of the detailed structure of the backlight control and image | video correction | amendment module which concerns on 2nd Embodiment. The block diagram which shows an example of a detailed structure of the backlight control and image correction module which concerns on 3rd Embodiment. It is a figure which shows an example of the characteristic of gain control and smoothing control. It is a block diagram which shows an example of the gradation smoothing processing module which concerns on 2nd and 2nd embodiment. It is a block diagram which shows an example of an internal structure of the micro change extraction part which comprises a gradation smoothing process module. It is a figure which shows the relationship between the input value Vi and output value Vo of a very small amount extraction part.

  The first to third embodiments will be described below with reference to the drawings. Basically, the following description is common to the first to third embodiments. FIG. 3 is a diagram showing an example of the backlight control / image correction module 69 of the first embodiment, and FIG. 10 shows the back of the second embodiment, which is different from the first to third embodiments. FIG. 11 is a diagram illustrating an example of a light control / video correction module (video signal processing device) 69, and FIG. 11 is a diagram illustrating an example of a backlight control / video correction module (video signal processing device) 69 according to the third embodiment. It is.

  First, a digital television receiver (liquid crystal television) 11 as an example of a video display device according to the first embodiment will be described with reference to FIG.

  The digital television receiver 11 includes a video display module 14, a speaker 15, an operation module 16, a light receiving module 18, broadcast signal input terminals 48 and 53, an analog signal input terminal 60, output terminals 63 and 64, and tuners 49, 54 and 56. , PSK demodulator 50, OFDM demodulator 55, analog demodulator 57, signal processing module 51, audio processing module 59, graphic processing module 58, video processing module 62, OSD signal generation module 61, control module 65, backlight control / A video correction module 69 and the like are provided.

  The broadcast signal input terminal 48 and the broadcast signal input terminal 53 are connected to a BS / CS digital broadcast receiving antenna 47 and a terrestrial broadcast receiving antenna 52, respectively. The light receiving module 18 receives a signal output from the remote controller 17.

  The control module 65 controls the operation of each unit in the digital television receiver 11. The control module 65 includes a CPU 70, ROM 66, RAM 67, and nonvolatile memory 68. The ROM 66 stores a control program executed by the CPU 70. The nonvolatile memory 68 stores various setting information and control information. The CPU 70 loads a command group and data necessary for processing into the RAM 67 and executes the processing.

  Operation information by the operation module 16 or operation information by the remote controller 17 received by the light receiving module 18 is input to the control module 65. The control module 65 performs control of each unit reflecting this operation content.

  The BS / CS digital broadcast receiving antenna 47 receives a satellite digital television broadcast signal. The BS / CS digital broadcast receiving antenna 47 outputs the received satellite digital television broadcast signal to the satellite digital broadcast tuner 49 via the input terminal 48. The tuner 49 selects a broadcast signal of a channel selected by the user from the broadcast signal. The tuner 49 outputs the selected broadcast signal to the PSK demodulator 50. A PSK (Phase Shift Keying) demodulator 50 demodulates the broadcast signal selected by the tuner 49 into a digital video signal and audio signal. The PSK demodulator 50 outputs the demodulated digital video signal and audio signal to the signal processing module 51.

  The terrestrial broadcast receiving antenna 52 receives a terrestrial digital television broadcast signal and a terrestrial analog television broadcast signal. The terrestrial broadcast receiving antenna 52 outputs a terrestrial digital television broadcast signal to the tuner 54 via the input terminal 53. The tuner 54 selects a broadcast signal of a channel selected by the user from the broadcast signal. The tuner 54 outputs the selected broadcast signal to the OFDM demodulator 55. An OFDM (Orthogonal Frequency Division Multiplexing) demodulator 55 demodulates the broadcast signal selected by the tuner 54 into a digital video signal and audio signal. The OFDM demodulator 55 outputs the demodulated digital video signal and audio signal to the signal processing module 51.

  The terrestrial broadcast receiving antenna 52 outputs a terrestrial analog television broadcast signal to a terrestrial analog broadcast tuner 56 via an input terminal 53. The tuner 56 selects a broadcast signal of a channel selected by the user from the broadcast signal. The tuner 56 outputs the selected broadcast signal to the analog demodulator 57. The analog demodulator 57 demodulates the broadcast signal selected by the tuner 56 into an analog video signal and audio signal. The analog demodulator 57 outputs the demodulated analog video signal and audio signal to the signal processing module 51.

  An input terminal 60 is connected to the signal processing module 51. The input terminal 60 is a terminal for inputting an analog video signal and audio signal from the outside to the digital television receiver 11. The signal processing module 51 converts the analog video signal and audio signal input via the analog demodulator 57 or the input terminal 60 into a digital video signal and audio signal, respectively.

  The signal processing module 51 performs predetermined digital signal processing on the converted digital video signal and audio signal, and the digital video signal and audio signal input from the PSK demodulator 50 or the OFDM demodulator 55. The signal processing module 51 outputs a video signal and an audio signal subjected to predetermined digital signal processing to the graphic processing module 58 and the audio processing module 59.

  Further, the signal processing module 51 includes a histogram calculation module 511. Among the video signals to be processed input to the signal processing module 51, the luminance signal (Y) is input to the histogram calculation module 511. The histogram calculation module 511 generates a histogram from the luminance signal (Y), and outputs the generated histogram to the backlight control / video correction module 69 via the control module 65 or the like.

  Specifically, the histogram calculation module 511 starts processing in response to the input of the video luminance signal (Y). The histogram calculation module 511 generates a histogram based on the luminance level of the pixels of the video signal. Specifically, the histogram calculation module 511 calculates the number of pixels for each luminance level for each frame of the video signal. In the following, it is assumed that the luminance level is divided into n stages. Note that the number n of luminance level divisions is sufficiently fine (for example, n = 256).

  The audio processing module 59 converts the input digital audio signal into an analog audio signal that can be reproduced by the speaker 15. The audio processing module 59 outputs this analog audio signal to the speaker 15. The speaker 15 reproduces sound based on the input analog sound signal. The audio processing module 59 may further derive an analog audio signal to the outside via the output terminal 64.

  The graphic processing module 58 superimposes an OSD signal such as a menu generated by an OSD (On Screen Display) signal generation module 61 on the digital video signal output from the signal processing module 51. The graphic processing module 58 outputs a video signal on which the OSD signal is superimposed to the video processing module 62. The graphic processing module 58 may selectively output the video signal that is the output of the signal processing module 51 and the OSD signal that is the output of the OSD signal generation module 61.

  The video processing module 62 converts the input digital video signal into an analog video signal that can be displayed on the video display module 14. The video processing module 62 outputs this analog video signal to the backlight control / video correction module 69. The video processing module 62 may further derive an analog video signal to the outside via the output terminal 63.

  The backlight control / video correction module 69 uses the analog video signal input from the video processing module 62 and the histogram input from the histogram calculation module 511 via the control module 65 to output the LED backlight control level (output). Brightness level) and the corrected video signal. Specifically, first, the backlight control / image correction module 69 analyzes a histogram of the luminance signal of the image, and based on the characteristics of this histogram, the variable width of the LED backlight control level, the LED backlight control level, and the like. The variable width of the correction amount (gain) of the video according to the change of the image is controlled. The characteristics of the histogram of the luminance signal are, for example, the dark area and the maximum luminance level. The dark area is the sum of the number of pixels corresponding to each luminance level smaller than the threshold, calculated based on the histogram. The maximum luminance level indicates the maximum luminance level among luminance levels in which the number of pixels is equal to or greater than a threshold value. The backlight control / image correction module 69 calculates an output luminance level corresponding to the input image signal according to the variable width of the LED backlight control level controlled based on the dark area. Further, the backlight control / video correction module 69 corrects the input video signal according to the variable width of the correction amount controlled based on the maximum luminance level. Then, the backlight control / video correction module 69 outputs the calculated LED backlight control level (output luminance level) and the corrected video signal to the video display module 14.

  The video display module 14 includes a liquid crystal panel 141 and an LED backlight 142. The liquid crystal panel 141 displays a video based on the corrected video signal. The corrected video signal is a video signal amplified by a gain determined based on the histogram. The backlight control / image correction module 69 controls the luminance levels of a plurality of LEDs (light sources) constituting the LED backlight 142 based on the LED backlight control level. That is, the backlight control / image correction module 69 can set the amount of light emitted from each of the plurality of LEDs toward the liquid crystal panel 141 according to the LED backlight control level.

  Here, the area control of the LED backlight 142 based on the LED backlight control level will be described. As described above, the LED backlight 142 includes a plurality of LEDs (light sources). Further, a video is displayed in a video area corresponding to the LED backlight 142, and this video area is defined to be composed of a plurality of partial areas. Then, it is defined that a light source block constituted by one or more light sources corresponds to a partial area. That is, a plurality of light source blocks correspond to a video area composed of a plurality of partial areas. Based on the LED backlight control level generated in accordance with the backlight control / image correction module 69 and the image signal (image luminance), the luminance of each light source can be divided and controlled in units of light source blocks.

  FIG. 2 is a block diagram for explaining an example of the arrangement of the backlight control / video correction module 69 in the digital television receiver 11. The backlight control / video correction module 69 is disposed, for example, at a position where the video display module 14 outputs a video signal subjected to various types of processing after all video processing on the input video signal is completed. .

  As shown in FIG. 2, the video processing module 62 outputs a video signal including a luminance signal (Y), a color difference signal (Cb), and a color difference signal (Cr) to the backlight control / video correction module 69. The backlight control / image correction module 69 has an appropriate output luminance level for each partial region indicating the minimum unit that can control the output luminance level of the LED backlight 142, and an image that has been corrected accordingly. Calculate the signal. The backlight control / video correction module 69 outputs the corrected video signal (RGB signal) to the liquid crystal panel 141. Further, the backlight control / image correction module 69 outputs an output luminance level (LED backlight control level) to the LED backlight 142.

  FIG. 3 is a block diagram showing an example of the configuration of the backlight control / video correction module 69. The backlight control / image correction module 69 includes an RGB conversion module 81, a spatial filter 82, a backlight control module 83, a gain control module 84, and a multiplier 85. The backlight control module 83 and the gain control module 84 are input with a histogram for each frame of the input video signal calculated by the histogram calculation module 511 described above.

  The RGB conversion module 81 converts the input video signal (luminance signal (Y), color difference signal (Cb), and color difference signal (Cr)) into an RGB signal that can be processed by the liquid crystal panel 141. The RGB conversion module 81 outputs the converted RGB signal to the spatial filter 82 and the multiplier 85.

  The spatial filter 82 performs area control of the LED backlight 142 in which a plurality of LEDs are arranged, and the planar light source attenuation characteristics corresponding to the partial area, which is the minimum unit of area control, and the partial area adjacent to the partial area The video signal is calculated in consideration of the influence (leakage of light, etc.) due to the planar light source corresponding to the above. The spatial filter 82 outputs the calculated video signal to the backlight control module 83.

  The backlight control module 83 includes a dark area calculation module 831, a backlight lower limit calculation module 832, a dimming start value calculation module 833, and a backlight level calculation module 834. The backlight control module 83 determines a backlight value (output luminance level) for each partial area.

  FIG. 4 shows an example of a conversion function representing the relationship between the input luminance level and the output luminance level. The conversion function between the input luminance level and the output luminance level is represented by, for example, a linear function 201 where input luminance level = output luminance level. In this case, the LED backlight 142 is set with an output luminance level (backlight value) as it is.

  However, in order to realize the power consumption reduction and the contrast expansion which are the features of the LED backlight 142, it is necessary to control the LED backlight 142 according to the characteristics of the video signal. In the first embodiment, the output luminance level of the LED backlight 142 and the gain for amplifying the video signal are controlled for each partial region in accordance with the characteristics of the video signal. For example, the backlight control module 83 sets the output luminance level of the LED backlight 142 to be small and sets the gain for amplifying the video signal to be large for the partial area to be controlled. In this case, power consumption can be reduced without changing the amount of light perceived by the user.

  In general, the power consumption of the LED backlight 142 is larger than the power consumption of the liquid crystal panel 141, and the ratio of the total power consumption of the digital television receiver 11 (liquid crystal television) is high. For this reason, suppression of the power consumption of the LED backlight 142 is highly effective in reducing the power consumption of the entire liquid crystal television.

  Further, when the LED backlight 142 is darkened, the image is darkened. In addition, except for the case where the entire partial area to be controlled has a constant brightness (luminance), the pixels in the partial area are distributed in various brightnesses (having various brightnesses). For this reason, the video signal is gain-corrected in accordance with the amount of darkening of the LED backlight 142, so that the brightest part of the partial area is kept as it is and the dark part is submerged (that is, the brightness is reduced). Can be suppressed). For example, when the brightness of the LED backlight 142 is controlled to ½, the brightness of the maximum luminance level (peak) can be made apparently the same by controlling the brightness of the video signal to be doubled. it can. In this way, it is possible to emit light firmly in the bright part of the screen and sink the dark part. Therefore, the contrast performance of the video display module 14 is superior to the contrast performance of a liquid crystal display device using a backlight with a uniform light source (for example, a cold cathode fluorescent lamp (CCFL)).

  However, depending on the backlight value set for each partial area, there may be a problem caused by light leakage from an adjacent partial area. For example, when the difference in backlight value between adjacent partial areas is large, there is a possibility that the darkness to be displayed cannot be obtained because the influence of light leakage on the darker partial area is large. In addition, in the case of an image with multiple light spots in the night sky such as fireworks, the backlight value is set according to this light spot, so the backlight cannot be fully stopped (the backlight value cannot be lowered). )there is a possibility.

  Therefore, the backlight control / video correction module 69 analyzes the luminance histogram of the video signal to calculate the dark area of the video, and represents the relationship between the input luminance level and the output luminance level according to the calculated dark area. Determine the conversion function. The backlight control / image correction module 69 changes the lower limit value of the backlight (output luminance level) and the dimming start value according to the dark area. That is, in a video having a large dark area such as a dark or night scene, an image with high contrast is generated by changing the conversion function aggressively. It should be noted that in a normal scene video (for example, a daytime scene or a bright indoor scene) with a small dark area, changes to the conversion function are suppressed, and settings are made so as not to cause problems.

  A function 202 shown in FIG. 4 is an example of a conversion function that represents the relationship between the input luminance level and the output luminance level used in the first embodiment. The function 202 is determined by the upper limit value (basic backlight value) and lower limit value of the output luminance level, and the dimming start value at the input luminance level.

  In the function 202, when the input luminance level takes a value from the maximum value of the input luminance level to the dimming start value, the output luminance level takes the upper limit value (basic backlight value) of the output luminance level. That is, a region (bright portion) with high luminance in the video is displayed with a specified backlight value. In the function 202, when the input luminance level is smaller than the dimming start value, the output luminance level decreases linearly from the upper limit value of the output luminance level toward the lower limit value as the input luminance level decreases. . That is, a low luminance area (dark part) in the video is displayed darker as the input luminance level becomes lower.

  As described above, the function 202 is determined by the upper limit value (basic backlight value) and lower limit value of the output luminance level, and the dimming start value at the input luminance level. A basic backlight value set using a menu screen or the like is input to the backlight control module 83. The backlight control module 83 sets the basic backlight value as the upper limit value (basic backlight value) of the output luminance level. Further, the backlight control module 83 determines the lower limit value of the output luminance level and the dimming start value at the input luminance level by analyzing the histogram calculated by the histogram calculation module 511.

  The histogram indicates the number of pixels for each luminance level obtained by counting the pixels included in the processing target video frame for each luminance level. The dark area calculation module 831 calculates the sum (cumulative value) of the number of pixels corresponding to each of the luminance levels smaller than the threshold, using the number of pixels for each luminance level. The calculated sum indicates the sum of the number of pixels in the low-luminance (dark) part, and is also referred to as a dark part area. As shown in FIG. 5, the dark area calculation module 831 calculates, for example, the sum of the number of pixels corresponding to each of the minimum luminance level to the sixth luminance level. Also, the dark area calculation module 831 calculates the sum of the number of pixels corresponding to each of, for example, a minimum luminance level (pedestal level) to a predetermined luminance level (for example, 20 IRE). The dark area calculation module 831 outputs the calculated dark area to the backlight lower limit value calculation module 832 and the dimming start value calculation module 833.

  In the first embodiment, since the darkest part sinks (darkness in which the darkest part is perceived by the user) and the dark part gradation (contrast), the ratio of the dark part area to the entire image (video frame) is emphasized. When is large, the lower limit value of the output luminance level is lowered, and the dimming start value is set large so that dimming is started from a large input luminance level.

  The backlight lower limit value calculation module 832 calculates the lower limit value (backlight lower limit value) of the output luminance level based on the dark area calculated by the dark area calculation module 831. The backlight lower limit value calculation module 832 acquires the lower limit value of the output luminance level corresponding to the dark area, for example, using a conversion coefficient as shown in FIG.

FIG. 6 shows an example of a conversion function representing the relationship between the dark part area D _lvl and the lower limit value BL _under of the output luminance level. In this conversion function, when the dark part area D _lvl takes a value from 0 to less than the threshold value, a predetermined value is set as the lower limit value BL _under of the output luminance level. Further, when the dark area D _lvl takes a value equal to or greater than the threshold value, a value that linearly decreases as the dark area D _lvl increases is set as the lower limit BL _under of the output luminance level.

  The backlight lower limit value calculation module 832 outputs the acquired lower limit value of the output luminance level to the backlight level calculation module 834.

  The dimming start value calculation module 833 calculates a dimming start value for starting dimming at the input luminance level based on the dark area calculated by the dark area calculation module 831. The dimming start value calculation module 833 acquires the dimming start value corresponding to the dark area, for example, using a conversion coefficient as shown in FIG.

FIG. 7 shows an example of a conversion function representing the relationship between the dark part area D _lvl and the dimming start value DIM _start . In this conversion function, when the dark part area D _lvl takes a value from 0 to less than the first threshold value, a first predetermined value is set as the lower limit value BL _under of the output luminance level. When the dark part area D _lvl takes a value less than the second threshold value from the first threshold value, the lower limit value BL _under of the output luminance level has a value that increases linearly as the dark part area D _lvl increases. Is set. In addition, when the dark part area D _lvl takes a value equal to or larger than the second threshold value, the second predetermined value is set as the lower limit value BL _under of the output luminance level.

  The dimming start value calculation module 833 outputs the acquired dimming start value to the backlight level calculation module 834.

  The backlight level calculation module 834 includes an upper limit value (basic backlight value) of the output luminance level input to the backlight control module 83, a lower limit value of the output luminance level calculated by the backlight lower limit value calculation module 832, and dimming The output luminance level for each partial region is determined according to the conversion function 202 of FIG. 4 determined by the dimming start value calculated by the start value calculation module 833. The LED backlight 142 turns on the light source (LED) corresponding to the partial area at the determined output luminance level for each partial area.

  For example, when an image having a dark area larger than the dark area calculated when the conversion function 202 is determined is input, the backlight lower limit value calculation module 832 is smaller than the lower limit value of the output luminance level. The dimming start value calculation module 833 calculates a larger value as the dimming start value. Therefore, when an image having a dark area larger than the dark area calculated when the conversion function 202 is determined is input, the backlight level calculation module 834 uses the conversion function 203, for example, to input luminance level. To determine the output luminance level. As shown in FIG. 4, the lower limit value of the output brightness level of the conversion function 203 is set to a value smaller than the lower limit value of the output brightness level of the conversion function 202. The dimming start value of the conversion function 203 is set to a value larger than the dimming start value of the conversion function 202.

  As described above, the backlight level calculation module 834 determines a conversion function for obtaining a corresponding output luminance level from the input luminance level according to the dark area calculated from the luminance histogram. Then, the backlight level calculation module 834 calculates the output luminance level for each partial region of the video using the determined conversion function. The backlight level calculation module 834 outputs the calculated output luminance level to the video display module 14 and the gain control module 84.

  The gain control module 84 includes a maximum luminance level calculation module 841, a gain maximum value calculation module 842, and a gain calculation module 843. The gain control module 84 calculates a gain for correcting the video signal according to the output luminance level calculated by the backlight level calculation module 834. The gain control module 84 sets the gain large when the output luminance level is lowered, and sets the gain small when the output luminance level is raised. That is, when the output luminance level (backlight value) is lowered, the input video is amplified (amplified) so as to keep the brightness of the pixel corresponding to the maximum luminance level (peak value) constant. However, since the luminance level (dynamic range) that can be displayed on the liquid crystal panel 141 is determined in advance, even if the video signal is amplified by gain, the luminance level exceeding the dynamic range may be saturated and displayed. . That is, the displayed video is crushed to the bright side, and video information is lost.

  In order to avoid this, the maximum luminance level calculation module 841 detects the maximum luminance level (bright portion maximum value) based on the luminance histogram calculated by the histogram calculation module 511. Then, the gain maximum value calculation module 842 calculates the maximum value of the gain used for correcting the video signal based on the maximum luminance level. Specifically, the maximum gain value calculation module 842 sets the maximum gain value so that, for example, when the maximum luminance level is large (close to the maximum dynamic range value), the video signal is not corrected by the gain. 1 (or a value close to 1) is set. That is, when the maximum luminance level is large, the maximum gain value is reduced in the gain adjustment performed on the video signal in response to the reduction of the backlight. As a result, a saturation phenomenon due to overcorrection on the video signal can be avoided.

  Hereinafter, a method for calculating the maximum gain value will be described.

  The maximum luminance level calculation module 841 determines the maximum luminance level (bright portion maximum value) in which the number of pixels is equal to or greater than a threshold from the histogram of luminance signals input from the histogram calculation module 511 (that is, the number of pixels for each luminance level). ) Is calculated. For example, as illustrated in FIG. 5, the maximum luminance level calculation module 841 searches for a luminance level in which the number of pixels is equal to or greater than a threshold value in order from the maximum luminance level, and calculates a bright portion maximum value. By searching for a luminance level in which the number of pixels is equal to or greater than the threshold, it is avoided that the luminance level corresponding to the pixel generated by noise is set to the bright portion maximum value. Then, the gain maximum value calculation module 842 calculates a gain maximum value that is a maximum value of gain for amplifying the video signal based on the determined bright portion maximum value.

FIG. 8 shows an example of a conversion function representing the relationship between the _bright portion maximum value B _lvl and the gain maximum value GAIN _max . In this conversion function, when the bright portion maximum value B _lvl takes a value from 0 to less than the threshold value, the gain maximum value GAIN _max is set to a value that decreases linearly as the _bright portion maximum value B _lvl increases. The When the bright portion maximum value B _lvl takes a value equal to or greater than the threshold value, a predetermined value (for example, 1.0) is set as the lower limit value BL _under of the output luminance level.

The gain maximum value calculation module 842 uses the conversion function representing the relationship between the bright part maximum value B _lvl and the gain maximum value GAIN _max as shown in FIG. 8 to _{obtain the} gain maximum value GAIN corresponding to the calculated bright part maximum value B _{lvl. max} is calculated.

The gain calculation module 843 corrects (amplifies) the video signal for each partial region based on the output luminance level for each partial region input from the backlight control module 83 and the calculated gain maximum value GAIN _max . Calculate the gain. The gain calculation module 843 outputs the calculated gain to the multiplier 85.

  The multiplier 85 corrects (amplifies) the RGB signal input from the RGB conversion module 81 based on the gain input from the gain calculation module 843. The multiplier 85 outputs the corrected RGB signal to the video display module 14.

  The liquid crystal panel 141 provided in the video display module 14 displays a video based on the corrected RGB signal. Further, the LED backlight 142 sets the amount of light emitted from each of the plurality of LEDs according to the calculated output luminance level (LED backlight control level), and lights these LEDs.

FIG. 9 is a flowchart showing an example of a procedure of backlight control processing by the backlight control / image correction module 69 using the histogram calculated by the histogram calculation module 511. The backlight control / image correction module 69 calculates the backlight lower limit value BL _under , the dimming start value DIM _start , and the gain maximum value GAIN _max based on the histogram.

  First, the histogram calculation module 511 generates a histogram for each frame from the input luminance signal (Y) based on the luminance level of the pixel (step S101). Specifically, the histogram calculation module 511 calculates the number of pixels Data (1) to Data (n) for each luminance level by counting the pixels for each frame included in the luminance signal (Y) for each luminance level. To do. n indicates that the dynamic range of the luminance is divided into n.

Next, the backlight control / image correction module 69 initializes a variable D _lvl for calculating the cumulative added value indicating the dark area (step S102). Specifically, the backlight control / image correction module 69 sets 0 to the variable D _lvl .

Next, the backlight control / image correction module 69 sets 1 to the variable i for the repetitive processing (loop A) (step S103). The variable i can take a value from 1 to D _lk . Note that D _lk represents the maximum luminance level that is the target of dark area calculation (cumulative addition value). Therefore, D _lk <n.

The backlight control / image correction module 69 adds the number of pixels Data (i) corresponding to the luminance level i to the variable D _lvl (step S104). Then, the backlight control / image correction module 69 determines whether or not the variable i is less than D _lk (step S105). When the variable i is less than D _lk , the backlight control / image correction module 69 adds 1 to the variable i and performs the processing in the loop A again. On the other hand, if the variable i is _greater than or _equal to D _lk , the backlight control / image correction module 69 ends the process of Loop A. At this time, the value set in the variable D _lvl indicates the dark area (cumulative addition value).

Next, the backlight control / image correction module 69 sets n to the variable j for the iterative process (loop B) (step S106). The variable j can take a value from n to 1. The backlight control / image correction module 69 searches the number of pixels for each luminance level in order from the higher luminance level by the process of loop B. Then, the backlight control and image correction module 69, a brightness level bright portion determination threshold TH _B greater than the number of pixels is set, sets the bright area maximum value. By using the bright part determination threshold TH _B , it is avoided that the luminance level corresponding to the pixel generated by noise is set to the bright part maximum value.

The backlight control / image correction module 69 sets j to the variable B _lvl for calculating the bright part maximum value (step S107). Then, the backlight control and image correction module 69 determines whether or not the pixel is greater than the number of Data (j) GaAkira portion determination threshold TH _B corresponding to the luminance level j (step S108). When the number of pixels Data (j) corresponding to the luminance level j is equal to or smaller than the bright part determination threshold TH _B (NO in step S108), the backlight control / image correction module 69 determines whether the variable j is greater than 1. Is determined (step S109). When the variable j is larger than 1, the backlight control / image correction module 69 subtracts 1 from the variable j and performs the process in the loop B again. On the other hand, when the variable j is 1 or less, the backlight control / image correction module 69 ends the process of the loop B.

Larger than the luminance level j in the corresponding number of pixels Data (j) GaAkira portion determination threshold TH _B (YES in step S108), the backlight control and image correction module 69, a dark portion area D as shown in FIG. 6 the conversion function indicating the relationship between the lower limit value _{BL under} the _lvl and the output brightness level, by substituting dark portion area _{D lvl} calculated in loop a, calculates the lower limit value _{BL under} the corresponding output luminance level (step S110 ).

Next, the backlight control / image correction module 69 substitutes the dark part area D _lvl calculated in the loop A into a conversion function indicating the relationship between the dark part area D _lvl and the dimming start value DIM _start as shown in FIG. Thus, the corresponding dimming start value DIM _start is calculated (step S111).

Then, the backlight control / image correction module 69 converts the bright portion maximum value B calculated in the loop B into a conversion function indicating the relationship between the bright portion maximum value B _lvl and the gain maximum value GAIN _max as shown in FIG. Substituting _lvl , the corresponding maximum gain value GAIN _max is calculated (step S112).

The backlight control / video correction module 69 sets the lower limit value BL _under , the dimming start value DIM _start , and the maximum gain value GAIN _max of the calculated output luminance level in each part in the backlight control / video correction module 69 ( Step S113).

Through the above-described processing, the backlight control / image correction module 69 determines the backlight lower limit value BL _under , the dimming start value DIM _start , and the maximum gain value GAIN _max according to the characteristics of the image. The backlight control / image correction module 69 determines a conversion function for calculating the corresponding output luminance level from the input luminance level based on the calculated lower limit value BL _under the output luminance level and the dimming start value DIM _start. . Then, the backlight control / image correction module 69 determines the output luminance level of the LED backlight 142 using the determined conversion function. Further, the backlight control / video correction module 69 corrects the video signal output to the liquid crystal panel 141 based on the determined output luminance level and the maximum gain value GAIN _max .

  As described above, according to the first embodiment, the contrast of the video can be improved by controlling the backlight based on the characteristics of the video signal. The backlight control / video correction module 69 changes the conversion function for calculating the corresponding output luminance level from the luminance level of the input video signal based on the characteristics of the video signal. The backlight control / image correction module 69 calculates a dark area indicating the size of the dark portion of the image based on the luminance histogram for each frame. Then, when the calculated dark area is large, the backlight control / video correction module 69 determines the conversion function so as to lower the lower limit value of the output luminance level and raise the dimming start value for starting dimming. The backlight control / video correction module 69 calculates a corresponding output luminance level from the luminance level of the input video signal using the changed conversion function. As a result, in the first embodiment, the sinking of the darkest part of the video (darkness at which the darkest part is perceived by the user) and the gradation (contrast) of the dark part can be expressed effectively.

  The backlight control / image correction module 69 detects the maximum luminance level of the image based on the luminance histogram for each frame. Then, the backlight control / video correction module 69 calculates a maximum gain value corresponding to the detected maximum luminance level. The backlight control / video correction module 69 calculates a gain for amplifying the video signal based on the output luminance level calculated using the conversion function and the calculated maximum gain value. Thus, in the first embodiment, it is possible to avoid saturation of the luminance level in the bright part of the video that occurs when the gain is calculated based only on the calculated output luminance level.

  The conversion function for calculating the corresponding output luminance level from the input luminance level may be data describing the correspondence between the input luminance level and the output luminance level.

(Second Embodiment)
Next, a second embodiment will be described with reference to FIG. FIG. 3 shows an example of the backlight control / video correction module 69 of the first embodiment, whereas FIG. 10 shows an example of the backlight control / video correction module 69 of the second embodiment. Show. Descriptions of parts common to the first embodiment (description of parts with the same reference numerals) are omitted.

  As shown in FIG. 10, the backlight control / image correction module 69 of the second embodiment includes a gradation smoothing processing module 86.

  The RGB conversion module 81 converts the input video signal (luminance signal (Y), color difference signal (Cb), and color difference signal (Cr)) into an RGB signal that can be processed by the liquid crystal panel 141.

  The spatial filter 82 performs area control of the LED backlight 142 in which a plurality of LEDs are arranged, and the planar light source attenuation characteristics corresponding to the partial area, which is the minimum unit of area control, and the partial area adjacent to the partial area The video signal is calculated in consideration of the influence (leakage of light, etc.) due to the planar light source corresponding to the above. The spatial filter 82 outputs the calculated video signal to the backlight control module 83.

  The backlight control module 83 determines a backlight value (output luminance level) for each partial area using a reference backlight level given by a user menu or the like as a reference value.

  The gain control module 84 controls the gain for correcting the video signal based on the backlight value. That is, the multiplier 85 corrects (amplifies) the video signal based on the gain controlled according to the change in the backlight value.

  For example, when a predetermined number of LEDs constituting the LED backlight 142 are controlled to have a low luminance, the partial video displayed in the partial area corresponding to the predetermined number of LEDs becomes entirely dark. If the partial video does not include a bright video (if the brightness of the partial video is uniform), it is possible to display such an overall dark partial video. However, if a bright video is included in this partial video (if the brightness of the partial video is not uniform), the display of such a partial video that is totally dark is originally bright in this partial video. The image that should have been darkened, is not an appropriate display.

  Therefore, as described above, the gain control module 84 controls the gain for correcting (amplifying) the video signal based on the backlight control level. For example, the gain control module 84 increases the gain according to the low luminance control based on the backlight control level. Thereby, the brightest part in the partial video described above is kept as it is, and the dark part can be sunk (that is, the brightness is suppressed). For example, when the brightness of the LED backlight 142 is controlled to ½, the brightness of the maximum luminance level (peak) is apparent by controlling the gain of the video signal to double the brightness of the video signal. Above, it can be the same. In this manner, the bright part in the screen is made to emit light firmly and the dark part is submerged, so that the contrast of the video display module 14 is higher than the contrast performance of a liquid crystal display device using a cold cathode fluorescent lamp (CCFL), for example. Performance can be increased.

  However, as described above, for example, even when the brightness of the LED backlight 142 is controlled to ½ and the gain of the video signal is controlled to double the brightness of the video signal, the gradation of the original video is It doesn't change. For this reason, the gradation level difference existing in the partial video is also amplified as it is. For example, when the brightness of the video signal is controlled to be doubled, the least significant 1 bit is not used. Furthermore, when the brightness of the video signal is controlled to 16 times, the least significant 4 bits are not used. When the entire image is dark, the sensitivity of the eyes is increased, so that the gradation difference is expanded, and as a result, the gradation difference may be easily recognized as a stripe.

  The backlight control / image correction module 69 can make such a difference in gradation inconspicuous by linking the gain control module 84 and the gradation smoothing processing module 86. For example, the tone smoothing processing module 86 controls a tone smoothing parameter that smoothes the tone of the video corresponding to the video signal in accordance with the gain controlled by the gain control module 84. That is, the gradation smoothing processing module 86 controls the effect of the gradation smoothing process using the gradation smoothing parameter in accordance with the change in gain controlled by the gain control module 84, and the gradation smoothing process allows the video signal to be processed. Smooth gradation. A multiplier 85 as an amplifying unit amplifies the video signal subjected to the gradation smoothing process based on the gain controlled by the gain control module 84.

  Regardless of the gain, when the gradation smoothing process by the gradation smoothing processing module 86 is applied to the video signal, the image may be lost and sharpness may be lost. Therefore, as described above, the effect of the gradation smoothing process is controlled according to the amplification level of the video signal, and the gradation smoothing process is applied to the video signal. Thereby, it is possible to prevent the above-mentioned image loss, sharpness reduction, and the like. For example, the gradation smoothing process may not be applied when the low luminance control is not performed based on the backlight control level, that is, when the video signal is not amplified.

  FIG. 12 is a diagram illustrating an example of characteristics of gain control and smoothing control. From the above-described relationship between the video signal and the backlight control level, the larger the designated value of the video correction amplification by the gain control module 84 is, the darker the video signal (the lower the luminance). For example, if the dynamic range of the signal input is 10 bits, 1024/64 = 16 in a state where a 64-fold amplification designated value is generated, and there are only 16 effective gradations of the original video. Become. As a result, the intensity of the gradation smoothing effect can be improved exponentially and the gradation can be secured as the amplification specified value for the image correction increases.

(Third embodiment)
Next, a third embodiment will be described with reference to FIG. FIG. 11 shows an example of the backlight control / video correction module 69 of the third embodiment.

  In the second embodiment, the multiplier 85 corrects (amplifies) the video signal after the gradation smoothing process by the gradation smoothing processing module 86. That is, the multiplier 85 amplifies the video signal subjected to the gradation smoothing process based on the gain controlled by the gain control module 84.

  On the other hand, in the third embodiment, after the correction (amplification) of the video signal by the multiplier 85, the gradation smoothing processing module 86 executes the gradation smoothing process on the video signal. In other words, the gradation smoothing processing module 86 performs gradation smoothing processing on the corrected (amplified) video signal based on the gradation smoothing parameter controlled according to the gain.

  As shown in the second embodiment, when the gradation smoothing process is executed prior to the correction (amplification) of the video signal, the effect of the gradation smoothing process is likely to be effective. Furthermore, since the gradation smoothing process can be applied before the amplitude of the video signal increases, the capacity of the line memory can be relatively small, and the circuit configuration of the backlight control / video correction module 69 can be relatively small. Can do.

  On the other hand, as shown in the third embodiment, when the correction (amplification) of the video signal is executed prior to the gradation smoothing process, the gradation smoothing process is applied after the correction (amplification) of the video signal. This makes it easy to obtain high-quality images.

  A fourth embodiment that combines the second embodiment and the third embodiment described above can also be implemented. In other words, gradation smoothing is applied to the video signal, and then the gradation smoothed video signal is corrected (amplified), and then the gradation smoothing is applied to the corrected (amplified) video signal. Apply processing. In this case, the effect of the gradation smoothing process is easily effective and a high-quality image can be obtained.

  According to the second, third, and fourth embodiments described above, the following video signal processing apparatus can be provided.

  The video signal processing apparatus can display an image with a high contrast effect while performing area control on the LED backlight 142. For example, two partial areas constituting the display area are adjacent to each other, the luminance level of the LED corresponding to one partial area (low luminance level), and the luminance level of the LED corresponding to the other partial area (high luminance level) Even in the case where the difference is large, the video signal processing apparatus can display a video with a high contrast effect. Even in the case of an image having a plurality of light spots in the night sky such as fireworks, the image signal processing apparatus can appropriately display an image with a high contrast effect. Conventionally, due to the influence of the light spot, the brightness of the backlight cannot be lowered sufficiently, and it has been difficult to display an image with a high contrast effect. It is also possible to suppress a video signal saturation phenomenon caused by excessive video correction caused by sufficiently reducing the luminance of the backlight.

  Next, an example of the gradation smoothing processing module 86 will be described with reference to FIGS. The gradation smoothing processing module 86 includes, for example, a vertical processing unit 105 and a horizontal processing unit 106.

  The vertical processing unit 105 processes the image signal (luminance signal Y) to reduce a gradation step in the vertical direction of the image. The horizontal processing unit 106 further processes the image signal processed by the vertical processing unit 105 to reduce a gradation step in the horizontal direction of the image. Here, the image signals are processed in the order of the vertical direction and the horizontal direction. It is also possible to reverse the order of this processing or to perform processing in parallel.

  The vertical processing unit 105 includes a frequency component decomposition unit 110, minute change extraction units 121 to 124, an averaging unit 130, and a subtraction unit SUBA, and reduces minute steps in the vertical direction.

  The frequency component decomposition unit 110 includes delay elements 111 to 118. The delay elements 111 to 118 are line memories, for example, and delay the luminance signal Y by one pixel in the vertical direction. Here, the pixel is delayed by one pixel in the vertical direction by delaying by the number of horizontal pixels Nv in the horizontal direction.

By using eight delay elements 111 to 118, a delay of ± 4 pixels is generated in the vertical direction. As a result, four sets of frequency components (A _−i , A ₀ , A _{+ i} ) are extracted (i = 1 to 4) with reference to the pixel signal A ₀ to be processed. As described later, it is possible to use five or more sets of frequency components.

The frequency components (A _−i , A ₀ , A _{+ i} ) are a set of pixel signals whose frequency components change from a short wavelength (high frequency) to a long wavelength (low frequency) in the order of the subscript i. The pixel signals A ₀ and A _{± i} mean pixel signals at the pixel P _{± i} that is shifted by the number of pixels ± i in the vertical direction from the pixel P ₀ and pixel P ₀ to be processed.

Since the pixel signals in the luminance signal Y are sequentially input to the frequency component decomposition unit 110, all the pixel signals become the pixel signal _A0 to be processed.

Each of the minute change extraction units 151 to 154 receives four sets of frequency components (A _−i , A ₀ , A _{+ i} ), and extracts a minute change amount near the pixel P _{0 in} each frequency component.

  FIG. 14 is a block diagram illustrating an example of an internal configuration of the minute change extraction units 151 to 154. The minute change extraction units 151 to 154 include subtraction units 171 to 173, a selector 174, absolute value calculation units 181 and 185, minute amount extraction units 182 and 186, a minimum value calculation unit 183, and a code return unit 184.

In accordance with the following equation (1), the subtraction unit 171 to 172, respectively, calculates the difference serving value C1~C3 pixel signals _{A -i, A 0, A +} i.

C1 = A ₀ −A _−i
C2 = A ₀ −A _{+ i}
C3 = A− _i− A _{+ i} (1)
Values C1, C2 refers to the amount of change in luminance of the pixel P _0, the value C3 is near the pixel P ₀ is meant whether the edge soaring or right shoulder. The selector 174 outputs the value D having the larger absolute value of the values C1 and C2.

The value D output from the values C3 and selector 174 refers to the amount of change in luminance in the vicinity of the pixel P _0. This amount of change may represent a luminance step. As will be described later, the outputs from the minute change extraction units 121 to 124 are averaged by the averaging unit 130, thereby having a meaning as a luminance step.

  The absolute value calculation units 181 and 185 calculate the absolute value of the value D and the value C3, respectively. This is because the signs of the values D and C3 are discarded to facilitate the processing by the minute amount extraction units 182 and 186.

  The minute amount extraction units 182 and 186 correct the values D and C3 and extract a minute amount.

  FIG. 15 is a diagram illustrating the relationship between the input value Vi and the output value Vo in the minute amount extraction units 182 and 186. Up to the reference value V1, the input value Vi and the output value Vo are equal (the input value Vi is output as it is). In this case, values up to the reference value V1 are extracted as steps as they are. When the input value Vi exceeds the reference value V1, the output value Vo is fixed to the reference value V1 (output rounding). That is, a value larger than the reference value V1 tends not to be extracted as a minute amount. Further, when the input value Vi exceeds the reference value V2 (folding value), the output value Vo becomes small and converges to 0 at the reference value V3.

  The input value Vi can be classified as follows according to the reference values V1 to V3.

(1) Extraction region (0 to V1)
In this area, the input value Vi is output as it is. That is, the input value Vi is extracted as a minute amount.

(2) Non-extraction region (<V3)
In this region, the input value Vi is not output. That is, the input value Vi is not extracted as a minute amount.

(3) Boundary region (V1 to V3)
This area is a boundary between the extraction area and the non-extraction area, and the input value Vi is reduced and output. This is a kind of buffer area. If the extraction region and the non-extraction region are directly connected, noise may occur in the image.

  This boundary region can be further divided into two regions.

a. Constant region (V1 <V2)
In this region, the output value Vo is constant (V1) regardless of the input value Vi.

b. Decrease area (V2 <V3)
In this region, the output value Vo decreases as the input value Vi increases.

  The reason for dividing the boundary region in this way is to smoothly connect the extraction region and the non-extraction region to prevent unnecessary noise from being generated in the image. Here, the boundary area is divided by a combination of two straight lines (linear function), but the boundary area may be divided by a combination of three or more straight lines. Further, the relationship between the input value Vi and the output value Vo in the boundary region can be expressed by a curve (multi-order function or the like). Further, the relationship between the input value Vi and the output value Vo including both the extraction region and the boundary region may be expressed by a curve (multi-order function or the like). In this case, the boundary between these regions is unclear.

As the reference amounts V1, V2, and V3, values suitable for the purpose of extracting a small amount are adopted. For example, when the maximum value of the value D is “2 ¹⁰ −1” (10 bits), the reference amounts V1, V2, and V3 may be 4, 5, and 9, for example. In this example, the ratios R1, R2, and R3 (V1 / Dmax, V2 / Dmax, V3 / Dmax) of the reference amounts V1, V2, and V3 with respect to the maximum value D are 3.9 × 10 ⁻³ and 4.9 ×. 10 ⁻³ , 8.8 × 10 ⁻³ . For the purpose of extracting a small amount, it is preferable that this ratio R1 is sufficiently smaller than 1. The ratios R1, R2, and R3 are set to about 1/100 and 1/50, for example. If the ratios R1, R2, and R3 are small to some extent, the reference amounts V1, V2, and V3 can be appropriately determined as necessary.

For example, when the maximum value of the value D is “2 ¹⁰ −1”, the reference value V1 can be set to 7, and the reference values V2 and V3 can be set to 7 and 16 accordingly.

  The minimum value calculation unit 183 outputs the smaller absolute value from the values Do and C3o corresponding to the values D and C3 extracted (corrected) by the minute amount extraction units 182 and 186. This is a measure for preventing the image from becoming noise by making the correction target value the smallest.

  Here, it is possible to integrate the functions of the minimum value calculation unit 183, the absolute value calculation unit 185, and the minute amount extraction unit 186 into the selector 174. This is because the minimum value calculation unit 183 selects a value from the values D and C3 that have been subjected to the same processing (absolute value calculation, minute amount extraction).

  When the function of the minimum value calculation unit 183 is integrated into the selector 174, the values C1 to C3 are input to the selector 174, and the value D is selected based on the following conditions (1) and (2) (minimum) The value calculation unit 183, the absolute value calculation unit 185, and the minute amount extraction unit 186 are omitted).

(1) When the absolute value of the value C3 is larger than the absolute value of any of the values C1 and C2 (| C3 |> | C1 |, | C2 |)
In this case, in the vicinity of the pixel P ₀ corresponding to the pixel signal A ₀ , the intensity of the pixel signal increases to the right or decreases to the right (increase or decrease). In this case, the larger absolute value is selected from the values C1 and C2. That is, based on the pixel signals A _0, who change amount is large are selected. The one with a larger absolute value is considered to represent the actual state of the luminance step.

(2) When the absolute value of the value C3 is smaller than at least one of the absolute values C1 and C2 (| C3 | <max (| C1 |, | C2 |))
In this case, in the vicinity of the pixel P ₀ corresponding to the pixel signal A _0, (not increasing, either a decrease) the intensity of the pixel signals around the pixel P ₀ is mountain-or valley become. In this case, the value C3 is selected as the value D. That is, the difference between the pixel signal A _{± i} of the pixel P _{± i} across the pixel P ₀ is selected. Since the pixel signal (luminance value) A ₀ itself at the pixel P ₀ is considered not to contribute to the luminance step in the image, it is ignored.

  The code returning unit 184 returns the code erased by the absolute value acquisition by the absolute value calculating units 181 and 185. As a result, the value E is output from the code returning unit 184 (the minute change extracting units 121 to 124). Note that outputs from the minute change extraction units 121 to 124 are values E1 to E4.

  As shown in the following equation (2), the averaging unit 130 averages the minute luminance changes E1 to E4 for each frequency component from the minute change extracting units 121 to 124, and further accumulates (1/2). Then, the value F is calculated. The value F has a meaning as a minute step of luminance in the vertical direction.

F = ((E1 + E2 + E3 + E4) / 4) / 2 Equation (2)
What is integrating the average value (1/2) is perpendicular to the pixel signal A _0, is taken into consideration to include the luminance step in the horizontal direction both. As will be described later, in the horizontal direction as well as in the vertical direction, values G1 to G4, which are minute changes in luminance for each frequency component, are calculated from the minute change extraction units 151 to 154. As shown in the following equation (3), the averaging unit 160 calculates a value H from these values G1 to G4.

H = ((G1 + G2 + G3 + G4) / 4) / 2 Equation (3)
The sum K (= F + H) of these values F and H has a meaning as a luminance step in both the vertical and horizontal directions. As shown in the following equation (4), this value K is the average of the minute changes E1 to E4 and G1 to G4 of the luminance for each frequency component both vertically and horizontally.

K = F + H = (E1 +... + E4 + G1 +... + G4) / 8 Equation (4)
As described above, (1/2) in the formula (2) is not in the pixel signal A ₀ vertically only considers to include the horizontal direction of the step.

  A minute step is obtained by this averaging. The luminance step is typically as follows. That is, the luminance changes between adjacent pixels, and the luminance before and after the pixel is kept substantially constant even if the pixels are different. That is, the luminance step appears in a range where the spatial frequency of the luminance is from a high frequency to a certain low frequency. As a result, by averaging the minute changes in luminance for each frequency component, the amount included in any of these components, that is, the luminance step is obtained as the value E.

  Here, the luminance step is extracted by averaging the minute changes at the spatial frequency in the range of ± 4 pixels. It is conceivable to widen the range of this spatial frequency. For example, it is conceivable to obtain an average for spatial frequencies in a range of ± 5 pixels or more. This means that a step is extracted based on a wider frequency component, which may improve the extraction accuracy.

  However, if the range of frequency components is excessively widened, the extraction accuracy may decrease. This is because it is highly possible that a component having a lower frequency than the frequency at which the luminance step appears does not include the luminance step to be extracted. For example, when a luminance step appears on the screen every 50 pixels, it is considered that the spatial frequency component in the range of ± 25 pixels or more does not include this step information.

  The averaging unit 160 averages the minute changes E1 to E4 without weighting. Here, as shown in the following equation (5), the value F may be calculated by weighting and averaging the minute changes E1 to E4.

F = (m1 * E1 + m2 * E2 + m3 * E3 + m4 * E4) / ((m1 + m2 + m3 + m4) * 2) (5)
Here, m1 to m4 are weights.

  The weights m1 to m4 are preferably large on the high frequency side and small on the low frequency side. As described above, the step included in the low-frequency component may be small.

Subtraction unit SUBA subtracts the value F from the pixel signal A _0, to remove components of the small level difference in the vertical direction from the original signal A _0. Thereby, the minute step reduction process with the vertical component is completed.

The horizontal processing unit 106 includes a frequency component decomposition unit 140, minute change extraction units 151 to 154, an averaging unit 160, and a subtraction unit SUBB, and processes the luminance signal processed by the vertical processing unit 105. The horizontal processing unit 106 reduces a minute step in the horizontal direction as in the vertical direction with the pixel signal B ₀ to be processed as a reference.

The frequency component decomposition unit 140 includes delay elements 141 to 148. The delay elements 141 to 148 delay the luminance signal Y by one pixel in the horizontal direction. By using the delay elements 141 to 148, a delay of ± 4 pixels is generated in the horizontal direction. As a result, based on the pixel signals _{B 0} to be processed, four sets of frequency components _{(B -i, B 0, B} + i) is extracted (i = 1~4).

Four sets of frequency components _{(B -i, B 0, B} + i) is input to the minimal change extraction section 151 to 154, small changes barrel value G1~G4 in luminance for each frequency component in the horizontal direction is calculated . In accordance with Equation (3), the averaging unit 160 calculates a value H, which is a slight level difference in luminance in the horizontal direction, from these values G1 to G4.

Subtraction unit SUBB subtracts the value H from the pixel signal B _0, to remove components of the small level difference in the horizontal direction from the pixel signal B _0. As a result, the vertical direction from the pixel signal A _0, is a minute difference in level of the luminance in the horizontal direction both been removed.

  Since the processing content in the horizontal processing unit 106 is not substantially different from that in the vertical processing unit 105, other detailed description is omitted.

  For example, when an image with a small number of gradations is visually observed, a slight brightness difference may be recognized. In particular, when a minute gradation step is arranged in a plain part such as a blue sky in an image, it is recognized by a human as a Mach band. The vertical processing unit 105 and the horizontal processing unit 106 reduce a minute step component from the luminance signal Y in both the vertical direction and the horizontal direction (smoothing of gradation steps). As a result, the Mach band in the image is reduced.

  When displaying an image with a low number of gradations with a high number of gradations, the fine step reduction processing in the vertical processing unit 105 and the horizontal processing unit 106 is particularly effective. The number of gradations that can be displayed on the display unit 108 may be larger than the number of gradations in the original image. In such a case, gradations that are not used in the original image can be used to reduce a minute step in the image. As a result, the fine step (Mach band) is reduced without destroying the detail information existing in the high frequency range.

  The reason why the number of gradations of the image itself does not match the number of gradations on the display unit 108 is, for example, the progress of multi-bit broadcasting signals. In other words, with the advance of technology (for example, miniaturization of semiconductor processes), multi-bit broadcasting signals and the like are being promoted. For example, the number of gradations of the broadcast signal is changed from 8 to 10 bits to 12 to 14 bits. In this case, image data created for a low-bit broadcast signal may be transmitted as a high-bit broadcast signal. Another reason for the discrepancy between the number of gradations of the image and the display is compression of information for improving transmission efficiency. That is, originally high-bit image data is rounded to low bits.

  The module described above may be realized by hardware, or may be realized by software using a CPU or the like.

  Note that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention in the implementation stage. In addition, the embodiments may be appropriately combined as much as possible, and in that case, the combined effect can be obtained. Further, the above embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, even if some configuration requirements are deleted from all configuration requirements shown in the embodiment, if the problem described in the column of the problem to be solved by the invention can be solved, the configuration in which this configuration requirement is deleted Can be extracted as an invention.

  69 ... Backlight control / image correction module, 81 ... RGB conversion module, 82 ... Spatial filter, 83 ... Backlight control module, 84 ... Gain control module, 85 ... Multiplier, 86 ... Tone smoothing processing module

Claims (10)

Gain control means for controlling the gain for correcting the video signal;
Gradation smoothing control means for controlling a gradation smoothing parameter for smoothing gradation of an image corresponding to the image signal in accordance with the gain controlled by the control means;
A video signal processing apparatus. Gradation smoothing processing means for applying gradation smoothing processing to the video signal based on the gradation smoothing parameter;
Amplifying means for amplifying the level of the video signal based on the gain;
The video signal processing apparatus according to claim 1, further comprising:   The video signal processing apparatus according to claim 2, wherein the gradation smoothing control unit controls the gradation smoothing parameter for controlling an effect of the gradation smoothing process according to a change in the gain.   The video signal processing apparatus according to claim 2, wherein the amplifying unit amplifies the video signal subjected to the gradation smoothing process based on the gain.   The video signal processing apparatus according to claim 2, wherein the gradation smoothing processing unit applies the gradation smoothing process to the amplified video signal based on the gradation smoothing parameter.   The gradation smoothing control means controls the gradation smoothing parameter so that the effect of the gradation smoothing process increases nonlinearly in response to an increase in the gain controlled by the control means. 2. A video signal processing apparatus according to 1.   The video signal processing apparatus according to claim 1, wherein the gain control unit controls the gain according to luminance control of a plurality of light sources corresponding to a video area for displaying the video.   The video signal processing apparatus according to claim 7, wherein the gain control unit controls the gain according to the luminance control corresponding to the video signal. A light source block constituted by one or more light sources corresponds to a partial area, a video area constituted by a plurality of light source blocks and a plurality of partial areas corresponds, and a unit of the light source block according to the video signal A light source luminance division control means for dividing and controlling the luminance of each light source,
The video signal processing apparatus according to claim 1, wherein the gain control unit controls the gain according to luminance division control of each light source. Control the gain to correct the video signal,
A video signal processing method for controlling a gradation smoothing parameter for smoothing gradation of an image corresponding to the video signal in accordance with the controlled gain.

Images